The aims of the proposed research are to study the mechanisms controlling passive transport and carrier-mediated transport across axon and vascular smooth muscle membranes. The immediate emphasis is directed towards an investigation of properties of the sodium-calcium countertransport in myelinated nerve, giant axons of Myxicola and vascular smooth muscle. The data of these investigations will be utilized to formulate kinetic models explaining the regulation of the intracellular calcium concentration in these tissues. Other investigations will be aimed at a determination of the types of ion selective channels in resting and excited nerve and muscle membranes, the permselective properties of these channels and the mechanisms controlling the permselectivity of these channels. The latter studies will be carried out on an internally perfused and voltage clamped giant axon of Myxicola.